Kinetic Study on the Inhibition of Xanthine Oxidase by Extracts from Two Selected Algerian Plants Traditionally Used for the Treatment of Inflammatory Diseases

In order to further understand and assess the validity of herbal medicine, we investigated the potential inhibitory effect of various extracts from Fraxinus angustifolia and Pistacia lentiscus, two plants used traditionally in Algeria against several inflammatory diseases such as rheumatism, arthritis, and gout, on purified bovine milk xanthine oxidase (XO) activity. The total phenolic contents of the leaves and bark of F. angustifolia and the leaves and seeds of P. lentiscus were estimated. P. lentiscus aqueous fractions from hexane and chloroform extractions and F. angustifolia aqueous fraction from ethyl acetate extraction inhibited XO activity by 72.74 +/- 2.63% (50% inhibitory concentration [IC50] 27.52 mu g/mL), 68.97 +/- 3.89% (IC50 = 42.46 mu g/mL) and 53.92 +/- 3.17% (IC50 58.84 mu g/mL), respectively, at 100 mu g/mL, compared to that of reference drug, allopurinol (98.18% [IC50 = 6.34 mu g/mL]). Moreover, at a concentration of 50 mu g/mL, both P. lentiscus extracts showed inhibition rates higher than 50%. F. angustifolia leaf extracts showed only mild inhibition. Lineweaver- Burk analysis showed that the inhibitory activity exerted by F. angustifolia bark aqueous extract and P. lentiscus aqueous extracts is of mixed type, whereas the leaf extracts from F. angustifolia inhibited XO noncompetitively. Positive correlations were established between XO inhibition and total phenols (r = 0.89) and flavonoids (r = 0.93) for P. lentiscus and with total phenols (r = 0.72) and tannins (r = 0.54) for F. angustifolia. Our findings suggest that the therapeutic use of these plants may be due to the observed XO inhibition, thereby supporting their use in traditional folk medicine against inflammatory- related diseases, in particular, gout.